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Subject: Re: [OMPI users] Performance do not scale at all when run jobs on same single node (Rocks, AMD Barcelona, Torque, Maui, Vasp, Openmpi, Gigabit Ethernet)
From: Aurélien Bouteiller (bouteill_at_[hidden])
Date: 2008-02-26 11:45:55

I think that ACML creates threads to fill all the available cores. If
you run 2 instances of ACML, it will create twice as many threads as
available cores and performances are obviously terrible. You should
check the ACML documentation to get the name of the environment
variable controling the number of threads ACML creates. As an example

Hope it helps,

Le 26 févr. 08 à 02:36, Steven Truong a écrit :

> Dear, all. We just finished installing the first batch of nodes with
> the following configurations.
> Machines: Dual Quad core AMD 2350 + 16 Gig of RAMs
> OS + Apps: Rocks 4.3 + Torque (2.1.8-1) + Maui (3.2.6p19-1) + Openmpi
> (1.1.1-8) + VASP
> Interconnections: Gigabit Ethernet ports + Extreme Summit x450a
> We were able to compile VASP + Openmpi + ACML and ran a bunch of
> tests. However, for all the tests that we ran a _single_ job on ONE
> node (1/2/4/8 core jobs) the performances of VASP jobs scaled well
> like what we expected.
> The problems have surfaced when we tried to run VASP jobs on the same
> node (like 2 4-cores jobs on 1 node) then we would see the performance
> degraded around a factor of 2. A sample VASP 4 cores test run on a
> single node (with no other jobs) would take closed to 900 seconds and
> for this same job, if we ran 2 instances of the same jobs on a single
> node, would would see around 1700-1800 seconds/job. On the compute
> nodes, I used top command and saw that all 8 threads were running
> (~100 %CPU) and the loads were around 8.0 and a little bit up to
> 8.5.
> I thought that processor and/or memory affinity needed to specify:
> #ompi_info | grep affinity
> MCA paffinity: linux (MCA v1.0, API v1.0, Component v1.1.1)
> MCA maffinity: first_use (MCA v1.0, API v1.0, Component
> v1.1.1)
> MCA maffinity: libnuma (MCA v1.0, API v1.0, Component
> v1.1.1)
> and in my job.txt file for qsub, I modified to include
> mpi_paffinity_alone:
> ....
> mpiexec --mca mpi_paffinity_alone 1 --np $NPROCS vaspmpi_barcelona
> ....
> However, with or without mpi_paffinity_alone, the performances still
> sucks pretty bad and are not acceptable. With mpi_paffinity_alone
> set, the performances were worse since as we observed with top command
> that some threads were idled a great deal of times. We also tried to
> run jobs without using qsub and PBS and used mpirun directly on the
> nodes, and the performance scaled well like running jobs on an
> isolated node. Weird?? What Torque + Maui could cause such problems?
> I am just wondering, what I have mis-configured my cluster: torque?
> vasp? maui? openmpi? Without the scaling issue, when jobs run with
> qsub and PBS, then things are great.
> My users's .bashrc have these 2 lines:
> export OMP_NUM_THREADS=1
> export LD_LIBRARY_PATH=/opt/acml4.0.1/gfortran64/lib
> and
> # ulimit -a
> core file size (blocks, -c) 0
> data seg size (kbytes, -d) unlimited
> file size (blocks, -f) unlimited
> pending signals (-i) 1024
> max locked memory (kbytes, -l) unlimited
> max memory size (kbytes, -m) unlimited
> open files (-n) 4096
> pipe size (512 bytes, -p) 8
> POSIX message queues (bytes, -q) 819200
> stack size (kbytes, -s) unlimited
> cpu time (seconds, -t) unlimited
> max user processes (-u) 135168
> virtual memory (kbytes, -v) unlimited
> file locks (-x) unlimited
> My Torque's nodes file has such a simple entry like this:
> compute-0-0.local np=4
> My Maui's setup is a very simple one.
> Please give you advices and suggestions on how to resolve these
> performance issues.
> Thank you very much.
> _______________________________________________
> users mailing list
> users_at_[hidden]

Dr. Aurélien Bouteiller
Sr. Research Associate - Innovative Computing Laboratory
Suite 350, 1122 Volunteer Boulevard
Knoxville, TN 37996
865 974 6321